1. Field of the Invention
The present invention relates generally to power transmission chains and link geometries for such chains. The invention has particular application to power transmission chains of the roller chain and silent chain variety for use in engine timing systems applications. The invention has specific application to such chain links that are utilized in an assembly with a chain tensioning system.
2. Description of the Prior Art
Power transmission chains are widely used in the automotive industry. Such chains are used for engine timing drives as well as for the transfer of power from the torque converter to the transmission or for the transfer of power in a transfer case. Power transmission chains are also widely used in industrial applications.
One type of power transmission chain is referred to as "silent chain". Such chain is formed of interleaved sets of inverted tooth links. A set or rank of links is assembled from several links positioned alongside of or adjacent to each other. The links are connected by pivot means, which are typically round pins received in a pair of apertures. An example of silent chain is found in U.S. Pat. No. 4,342,560, which is incorporated herein by reference.
Conventional silent chains typically include both guide links and driving links. The guide links are positioned on the outside edges of alternate sets of links. The guide links typically act to position the chain laterally on the sprocket. Guide links do not act in the transfer of power between the chain and the sprocket.
The inverted tooth links, or inside or driving links, provide the transfer of power. Each link typically includes a pair of apertures and a pair of depending toes or teeth. Each toe is defined by an inside flank and an outside flank. The inside flanks are joined in a crotch. The links contact the sprocket teeth along the inside flanks or outside flanks or combinations of the two. The contacts between the flanks and the sprocket teeth can be of the type which provide a power transfer.
The backs or upper edge of the links, which are not typically involved in the transmission of power, are generally straight or convexly (outwardly) curved. In a chain of the hybrid type, that is, a type having more than one or configuration or type of link, the links may be identified by the shape of the backs of the links. U.S. Pat. Nos. 4,509,323 and 4,509,937 are examples of such link back shapes being used for link identification.
A second type of chain is known as "roller chain". A typical roller chain consists of alternate inner links and outer links. The inner links, which are also known as "bushing" links, consist of spaced sidebars with bushings tightly received in openings, or apertures, at each end of the sidebars. The outer links, which are also know as "pin" links, consist of spaced sidebars with pins tightly received in openings, or apertures, at each end of the sidebars. The bushings freely rotate about the pins to pivotally connect the outer links to the inner links in alternate arrangement. Rollers are provided on the bushings, and when the roller chain is wrapped about a sprocket, the teeth of the sprocket are received between the laterally spaced sidebars and the longitudinally spaced rollers. An example of roller chain is found in U.S. Pat. No. 4,186,617, which is incorporated herein by reference.
Roller chain drives can include both "true roller" and rollerless design. The true roller design includes the described rollers mounted about the bushings. Rollerless chain contains bushings that directly contact the sprocket. Both types of roller chain are typically specified in industry as British Standard chain and American National Standards Institute (ANSI) chain.
A conventional chain drive is comprised of an endless silent or roller chain wrapped about at least two sprockets supported by shafts. Movement of a driving sprocket causes power transmission through the chain and consequent movement of a driven sprocket. In an engine timing drive application, the driving sprocket may be mounted on the engine crankshaft and the driven sprocket mounted on a valve camshaft. The rotation of the camshaft is thus controlled by the rotation of the crankshaft through the chain.
Many timing chain applications typically include a resiliently-biased chain tensioner positioned externally of the chain between the spaced sprockets. The tensioner acts to control chain tension during operation by providing a load against the back surfaces of the links of the chain assembly. A contact surface area is typically provided along the tensioner for contacting the chain. The tensioner can be placed on either the tight side or the slack side of the chain but is typically placed on the slack side.
The chain links in an assembly for use with a tensioner typically have flat or convex back surfaces. In a silent chain, the back of the link is the upper portion of the link. In a roller chain, the back of the link is the elongated portion of the side bars that extends between the apertures. As a consequence of the flat back surfaces, the links will have high contact stresses over a limited contact area between the tensioner contact surface area and the back of the chain link. Such contact stresses provide frictional losses which reduce the efficiency of the chain drive system.
More recent silent chain assembly designs, such as those shown in U.S. Pat. No. 4,758,210, which is incorporated by reference, have a reduced number of links in each row in order to decrease the width of the chain. This increases the loading on each link in the chain assembly. Moreover, the requirements for increasing engine speeds and, consequently, increasing chain drive speeds, have increased the localized frictional contacts between the chain links and the tensioner, and provided even greater inefficiencies.
The present invention acts to reduce the above-mentioned frictional contacts between the chain tensioner and the chain link through an improved chain link design.